Sleep Tight
Simply meaning to ‘sleep well,' the phrase “sleep tight” dates back to the time when mattresses were supported by ropes as opposed to springs. The method used to create a comfortable surface to lie on was to stretch ropes across from side to side of the bed-frame in a crisscross pattern. After a while of use, the ropes stretched and sagged, and it was necessary to tighten them from time to time in order to sleep comfortably.